Coated abrasive products



Dec. 26, 1961 scHMlDLlN 3,014,795

COATED ABRASIVE PRODUCTS Filed June 12, 1959 \[I IIIIIIIIIIIIIII/I/IrJ ff f f Q 0 O O U United States Patent 3,014,795 CQATED ABRASIV E PRODUCTSHerbert L. Schmidlin, Packanack Lake, N.J., assignor toRaybestos-Manhattan, Inc., Passaic, N.J., a corporation of New JerseyFiled June 12, 1959. Ser. No. 819,941 6 Claims. (Cl. 51-297) example,the small abrasive disks provided with reatively stiff paper backingelements so popular in the dental trade are hazardous to use because ofthe danger of tearing or breaking and thereby causing injury to thepatient. Vulcanized fiber disks are also used for this purpose but arenot suitable because of the excessive thickness required to obtainadequate strength. For general use the available paper backed coatedabrasive sheets are too weak and easily torn to be efliciently useful.In certain finishing app'ications that require a thin abrasive sheet,problems of strength and heat resistance are encountered which are illsatisfied by the commercially available products. Known fabric backedcoated abrasive sheets are found to be too thick and inflexible tosatisfactorily finish contour work.

The prime object of my present invention pertains to the provision of acoated abrasive product which may efiectively serve in the mentionedspecialized applications for which known flexibly backed abrasiveproducts are generally deficient, and one which'is also efiicientlyuseable .for general applications.

More specific objects of the invention are the provision of a coatedabrasive sheet provided with a tough, flexible tear-resistant backing;the provision of a plastic backed coated abrasive sheet having improvedheat resisting properties; the provision of thin flexible coatedabrasive products used for finishing and polishing which are strong,tough and tear-resistant; and the provision of relatively .stiff butflexible coated abrasive products which combine the properties oftear-resistance and heat-resistance.

To the accomplishment of the foregoing objects and such other objects asmay hereinafter appear my invention relates to the coated abrasiveproducts as sought to be defined in the appended claims and as describedin the foflowing specification taken together with the accompanyingdrawings in which:

FIG. 1 is a perspective view of a coated abrasive product embodying thestructure of the present invention;

FIG. 2 is an enlarged view thereof taken in crosssection in the plane ofthe line 2-2 of FIG. 1; and

FIG. 3 is a schematic view depicting the manner of making a Mylarfilm-fibrous web lamina for use in making the coated abrasive product ofthe invention.

I have found that a tear-resistant but thin flexible coated abrasiveproduct in the form of a sheet or disk possessing suitable heatresistance may be made by using a backing element for the productcomposed of a fibrous web layer laminated to a Mylar polyester film.Mylar is a poyester film made from polyethylene terephthalate-- thepolymer formed by the condensation reaction between ethylene glycol andterephthalic acid. The fibrous web layer may be, for example, rag paper,rope paper, kraft paper or glass fibre. The fibrous web layer serves asthe carrier for the layer of abrasive grains which latter are resinembedded and bonded, the bonded abrasive layer ice being united by themaker or bond resin to the fibrous web. The fibrous web is laminated tothe Mylar film by a thermoplastic or modified thermopastic resinadhesive.

The fibrous web then also serves the purpose of insulating thethermoplastic adhesive on the Mylar film from frictional heat in use.The Mylar film imparts the property of tear-resistance to the abrasiveproduct.

The thinness of the fibrous web-Mylar film laminate is selected inaccordance With the degree of stiffness desired in the abrasive sheet. Adesirable tear-resistant but thin and flexible product with suitableheat resistance can be made by using a backing elementcomposed of a.

fibrous web, which may be as thin as 2 mils or as thick as 20 mils,laminated to a film of Mylar having a thinness of from 0.5 to 3.0 mils.The adhesive for uniting the fibrous web to the Mylar film may be anysuitable thermoplastic resin or modified thermoplastic resin (i.e. onecombined with a thermosetting type resin) that adheres well to theplastic Mylar film, such as an a kyd or modified alkyd resin or anacrylonitrile-phenolic resin.

The maker or binder resin for embedding the abrasive grains and unitingthe same to the fibrous web, where an optimum heat resistant product isdesired, is a heat-hardened thermosetting resin such asphenolformaldehyde, urea-formaldehyde or melamine-formaldehyde. resin.Where an abrasive product of greater flexibility and suppleness isdesired, the maker resin may comprise a urethane elastomer as describedin the copending application of Joseph N. Kuzmick, S.N. 739,933, filedJune 4, 1958, such urethane e'astomer comprising the non-foaming groupof polyol isocyanate products in solid or liquid phase, which, forexample are made from diisocyanates and a linear polyester such asethylene glycol adipate. When such a urethane elastomer is used as themaker or binder resin, the fibrous web consists preferably in astretchable paper such as the extensible kraft paper made by theso-called Clupak process.

Referring now more in detail to the drawings and having reference firstto FIG. 3 thereof wherein is depicted schematically a method of makingthe laminate employed as the backing element for the abrasive coatedproduct, the Mylar lamina is shown fed from the supply roll 10 into andthrough a reverse roll-coater 12 for the application of an adhesive tothe top surface of the Mylar sheet or film 14, the adhesive coated Mylarfilm then being fed through an air drying oven 16 (to remove solvents),the coated film being thereafter bounded to a fibrous web 18 deliveredfrom a supply roll 20, the fibrous web and the Mylar film beinglaminated at the nip of the bonding rolls 22 after which the laminate isfed to and reeled on the take-up roll 24.

The laminate thus produced is then coated on its fibrous web side withthe maker or bonding resin for the abrasive grains after which theabrasive grains are sprinkled on the surface of the binder and theproduct is then subjected to the usual heat curing cycle. The resultingproduct comprises, as shown in FIGS. 1 and 2, the coated abrasive sheetwhich comprises a layer of abrasive grains 26 embedded in the makerresin 28 and united to the flexible backing sheet which consists of thefibrous web or layer 30 adhesively laminated to the Mylar polyester film.32, the abrasive grain layer being bonded to the fibrous web by themaker resin.

The following are typical specific examples of practising the presentinvention.

Example I As an example of the practice of the invention I take a Mylarpolyester film one or two mil thin. As aforesaid Mylar is a polyesterfilm made from polyethylene terephthalate-the polymer formed by thecondensation reaction between ethylene glycol and terephthalic acid.

Mylar polyester film manufactured by Du Pont is an excellent example, asthis film is extremely strong and tear resistant, can be deformed andeven stretched, and is resistant to water and many solvents and isserviceable at temperatures up to 350 F. The fibrous web layer may be ofrag paper that is relatively thin, dependent upon the amount ofstiffness desired in the product; and in this example the rag paper is 7mils thick. On the surface of the fibrous web layer of the 'Mylar paperlaminate there is spread a phenol aldehyde resin of the characterhereinabove described; and following the spreading of this binderabrasive grain, such as silicon carbide, alumina, flint or garnet issprinkled on the surface of the binder. The motion of the abrasivecoated product thus produced is continued over suitable supportingrolls, inverted to permit excess abrasive above that attached to thesurface by adhesion to he binder to fall off, and the coated film ismoved through a tunnel oven heated at 300 'F., the product being therebysubjected to the usual heat curing cycle. The product thus produced issubsequently cut into sheets, disks, or belts to provide the desired endproduct.

The mesh size of the abrasive grains may be varied depending upon thethickness of the end product desired and a range of mesh size mayinclude the fine #500 mesh screen to the coarse #80 mesh screen size. Asis customary in making coated abrasive products employing aheat-hardened resin as the maker or hinder resin, a barrier coat mayfirst be applied to the fibrous web prior to applying the maker resincoating thereto. The thickness of the makerresin layer may be variedfrom /2 mil, dried film basis (for fine grit) to 3 mils, dried filmbasis (for coarser grit). The abrasive layer thickness is controlled bythe viscosity and film thickness of the applied maker resin. With a thinmaker resin coating the abrasive grit may deposit only one particlethick. With greater amounts of resin the number of abrasive layers willincrease to several particles thick. The abrasive layer thickness willdepend on the wetting quality of the resin. A nominal thickness of fine400 grit abrasive may be 2 or 3 mils. For 100 grit the abrasive layermay be 5 to mils thick.' The time-temperature heating cycle may bevaried as is customary depending upon the character of the thermosettingheat hardenable resin employed.

As a variant of this example the fibrous web lamina may be athin sheetof rope paper in which a 4 mil thick rope paper is used. Another type offibrous web that may be employed is kraft paper; it may be pointed outthat except for the low grade flint coated type of sandpaper, kraftpaper would not for ordinary applications be considered suitable for acoated abrasive product. By the method of the present invention a filmof Mylar to which is laminated kraft paper produces a backing elementthat has the desired physical properties of strength, toughness andflexibility that could not otherwise be obtained wtihout costlyspecialized manufacturing processes.

Example II This example illustrates the application of the invention tothe making of an abrasive product of increased flexibility andsuppleness. For this purpose/the maker resin comprises a urethaneelastomer, in this instance a product sold as Adiprene manufactured byDu Pont. This urethane elastomer is compounded or mixed with 12% byweight of a cross-linking agent dichlorobenzidene. Adiprene is a liquidurethane elastomer reaction product of diisocyanate and a polyalkyleneether glycol. Following the spreading of the binder, a #200 mesh siliconcarbide abrasive is sprinkled on the surface of the binder. Theoperations as described in Example I are carried through, the curingcycle being at 250 F. for a period of 30 minutes. In this example thefibrous web is an extensible kraft paper made by the Clupak process; thestretch properties of this type kratt paper makes it particularlydesirable to use as a lamina for making an extremely flexible andtear-resistant coated abrasive product.

The coated abrasive products of the present invention and the manner ofmaking the same and their functioning in various abrasive applicationswill it is believed be apparent from the above description thereof. Itwill be further apparent that many changes will be made withoutdeparting from the spirit of the invention as defined in the followingclaims.

1 claim:

l. A thin flexible coated abrasive product combining the properties oftear resistance and heat resistance consisting as the essential elementsof a layer of abrasive grains deposited onto and embedded in a syntheticmaker resin, said maker resin coated onto and united to a tough flexibletear resistant backing sheet, said backing sheet consisting of a fibrousweb adhesively laminated to a polyester film of polyethyleneterephthalate, the abrasive grain layer being" united to the fibrous webside of said backing sheet and being bonded by said maker resin to thefibrous web of said backing sheet.

2. The coated abrasive product of claim 1 in which the abrasive grainembedding resin is a thermosetting heathardened resin. J

3. The coated abrasive product of claim 1 in which the abrasive grainembedding resin is a non-foamed polyurethane elastomer.

4. The coated abrasive product of'claim 1 in'which the laminatingadhesive is a thermoplastic resin.

5. The coated abrasive product of claim 1 in which the abrasive grainembedding resin is a thermosetting'hcathardened resin and the laminatingadhesive is a thermoplastic resin. 7

6. The coated abrasive product of claim 1 in which the fibrous webcomprises a fabric selected from the class consisting of rag paper, ropepaper, kraft paper, extensible kraft paper and glass fiber.

References Cited in the file of this patent UNITED STATES PATENTS,

R'osSer Mar. 25, 1958

1. A THIN FLEXIBLE COATED ABRASIVE PRODUCT COMBINING THE PROPERTIES OFTEAR RESISTANCE AND HEAT RESISTANCE CONSISTING AS THE ESSENTIAL ELEMENTSOF A LAYER OF ABRASIVE GRAINS DEPOSITED ONTO AND EMBEDDED IN SYNETHETICMAKER RESIN, SAID MAKER RESIN COATED ONTO AND UNITED TO A TOUGH FLEXIBLETEAR RESISTANE BACKING SHEET, SAID BACKING SHEET CONSISTING OF A FIBROUSWEB ADHESIVELY LAMINATED TO A POLYESTER FILM OF POLYETHYLENETEREOHTHALATE, THE ABRASIVE GRAIN LAYER BEING UNITED TO THE FIBROUS WEBSIDE OF SAID BACKING SHEET AND BEING BONDED BY SAID MAKER RESIN TO THEFIBROUS WEB OF SAID BACKING SHEET.